The present invention relates to a method of writing a file to a plurality of media and a storage system thereof and more specifically, the present invention relates to a method of writing a plurality of parts of a file to a plurality of tape media in a storage system which includes at least two tape drives.
The data storage capacity of a storage system which includes a tape drive depends on a maximum capacity of a tape medium used in the tape drive, which serves as an upper limit of the storage capacity. For a fifth generation linear tape open (LTO) tape drive, for example, an amount of data exceeding about 1.5 TB, which is the maximum capacity of the medium, is not capable of being written. Furthermore, when additional data is to be written to a medium which already has some amount of data stored thereto, the amount of the data that is able to be additionally written is less than the maximum capacity of the medium.
A tape drive may be used in a file system, along with a hard disk drive (HDD) and the like. For example, a linear tape file system (LTFS) is an example of one file system for tape drives. When the LTO data is handled as a file in the LTFS, again, the amount of data that may be additionally written is less than the capacity of the tape medium.
Due to recent storage utilization demands, the amount of data desired to be written to a medium has been steadily increasing. In some cases, a total size of a file to be written may be uncertain at the time that the file starts being written. For example, the size of a file to be written is uncertain when the file starts being written during a program recording that is conducted in real time in the broadcasting industry, or where a sequence of video from a universal serial bus (USB) camera in a security system is directly written to a medium. In such cases, the size of the file to be additionally written to the medium may exceed the capacity of the medium without any warning prior to beginning writing the file. If this occurs, the file written up to the moment must be separately saved, and the subsequent data must be written to another medium (known as “spanning”). Currently, there is no method or mechanism capable of achieving spanning in the LTFS.
Japanese Patent Application No. JP11-306190A discloses a technique for rearranging system information so as to write the system information to one medium in order to avoid loading all the media and referring to system information for file management when the system information is distributed among a plurality of media.
However, Japanese Patent Application No. JP11-306190A does not take into consideration a case where a medium is not large enough to hold an entire file to be written and also does not disclose that attribute information of a file is saved in a first medium. Because it takes a very long time to unload and load a tape cartridge (medium), it is essential to reduce the number of times that a tape medium is unloaded and loaded in order to improve the performance of reading a large file.